Built for speed: molecular properties of the voltage sensor domain underlie the rapid activation of voltage-gated Na(+) channels compared with Shaker-type K(+) channels.

Many of us were taught in high school biology that the action potential waveform in nerves and other excitable tissues was generated by an initial rapid influx of external Na(+) ions across the plasma membrane, followed by an outward movement of intracellular K(+) ions. The former event, mediated by voltage-gated Na(+) channels, is responsible for the fast depolarizing upstroke of the action potential, while voltage-gated K+ channels are responsible for the subsequent repolarizing phase, which largely controls action potential duration. Although Hodgkin and Huxley described the fundamental importance of this sequential activation process more than 60 y ago, the molecular and structural details underlying the faster activation of voltage-gated Na(+) (Nav) vs. K(+) (Kv) channels have yet to be fully resolved.